Renal function in hydroelectrolytic homeostasy will be studied; particularly: mechanism of isotomic reabsorption in the proximal tubule, role of the collecting duct in phosphate reabsorption in presence and absence of parathormone, mechanism of renal action of clonidine, role of prostaglandins in renal concentrating mechanism, magnitude of urea synthesis by the kidney. These problems will be studied by using methods of microphysiology electron probe microanalysis of liquid droplet and frozen hydrated tissue and a microfluorometric method allowing for fluorometric measurements in picoliter volume samples.